Here is some beach controversy. Perhaps I’m a bit of a Libertarian in this regard, but it seems to me that tents shouldn’t be a problem. I’d weight the importance of sun protection over possible shenanigans in the tents. It would seem just as easy to patrol that as the tents themselves.

REHOBOTH BEACH, Del.—Capt. Kent Buckson’s radio crackled with word of a situation on the beach. A lifeguard had spotted a large canopy amid the sea of umbrellas. That meant one thing. Time for a takedown.

“We’ve got to get to that one,” said Mr. Buckson, the soft-spoken beach patrol boss. He and his deputy, Aaron Tartal, jumped into an all-terrain vehicle and headed over. Mr. Tartal, shirtless and in red swim trunks, strode over to the canopy owner.

“Good morning, sir. I’ve got bad news,” Mr. Tartal told the man. Then he laid out the new law on the two-mile beach. No tents or canopies allowed, except baby tents up to 3 feet high, wide or deep.

“Freakin’ ridiculous,” groused the man, who declined to give his name, as he dismantled the black 8-by-10-foot canopy he had just erected.

“New city ordinance, it’s a little bit of a learning curve,” Mr. Tartal gamely replied, pointing out the nearby shacks that rent umbrellas for $12 a day.

Rehoboth Beach is part of a wave of seaside communities that have embraced umbrella-only policies. Myrtle Beach, S.C., enacted such a law four years ago. This summer, Sunset Beach, N.C., and Seaside Heights, N.J., both rolled out regulations restricting sun shields in some places.

Myrtle Beach’s advice to Rehoboth Beach: Hang in there. “The first year was fairly rocky,” spokesman Mark Kruea said. “People are accustomed to having that tent.” While the South Carolina resort sometimes cites people for wearing overly skimpy swimsuits, he couldn’t recall anyone being ticketed for violating the canopy law.

Since May 27, the Rehoboth beach patrol says, lifeguards have blown the whistle on canopies and tents about 840 times—“takedowns,” Mr. Buckson calls them. Lifeguards can call police if a violator doesn’t comply, though police have issued just three $25 tickets, according to Rehoboth Beach Police Chief Keith Banks.

For the 65 lifeguards, many of them college age, it has been a different kind of educational experience. Their diplomacy skills are tested as front-line enforcers of a law that can pull unsuspecting beachgoers into an undertow of anger and disbelief.

“We keep it short and simple,” said 21-year-old lifeguard Ryan Crowley. “Captain B. doesn’t want us getting into altercations.” Some people already were giving them lip for enforcing bans on smoking, drinking and kite-flying, he said.

Fans view the law as a fair way to improve the beach experience. Critics throw shade, calling it a pointless hassle and questioning why a cluster of umbrellas is OK if open-sided canopies aren’t. Some wonder if the aim is to boost umbrella rentals. (It isn’t, officials say.)

“It’s definitely a hot potato,” said Mr. Buckson, 50 years old, who has led the beach patrol for 18 years and also is a special-education teacher. His voice rose at one point during an interview, prompting him to say, “It’s stressful, as you can maybe tell from my voice.”

Rehoboth Beach officials say public safety and aesthetics drove the change. Large, “nontraditional shading devices” had mushroomed in recent years, making it harder for lifeguards to see the beach and water while impeding access to the ocean, they say. Some people used the fabric walls to hide smoking or alcohol consumption.

Officials say single-pole umbrellas pose less of a navigational challenge for lifeguards and first-responders than canopies or tents with multiple poles and in some cases tethers.

Another concern: High wind could turn poorly anchored tents and canopies into airborne projectiles, though Mr. Banks acknowledged umbrellas present a similar risk.

Dozens of visitors and residents had complained about tents and canopies to the local Chamber of Commerce, said its chief executive, Carol Everhart, who notified the town. She said public support for the law seems strong.

“Love, love, love it,” said regular visitor Lynn Degenhart as she sat on the beach with her husband, Karl. The beach is now much less cluttered, she said. She used a baby tent to shade their cooler.

“Just remember, if you see the pop-up tents or canopies, approach the people politely” and “ask them please take them down within the next 15 minutes,” he said. “They’re not going to be too happy about it.”

The first takedown fell to 19-year-old Christian Cosden. The offenders were Justin and Sara Slomkowski of Philadelphia, whose umbrella had a swatch of fabric extending down to the sand to shade their 16-month-old, Nora.

Mr. Cosden, shirtless and barefoot, explained that umbrellas with sides aren’t allowed. “So if you can take the sides off, that’d be awesome,” he said.

“Sure,” said Mr. Slomkowski.

“Cool. Thank you, guys.”

Asked about it, Mr. Slomkowski said it was “kind of silly” they had to yank the side off. His wife bought the umbrella after reading about the law online and thought it complied. They weren’t going to make waves. “We’re just here on vacation for a couple days,” he said.

Mr. Cosden said most interactions are similarly smooth, but some scofflaws tell him to go pound sand. “They just won’t take it down, they just won’t even talk to you or look at you, or they’ll walk away,” he said. Those he lets the police handle.

That morning, the beach patrol’s Mr. Tartal broke it to John Haas of Silver Spring, Md., that his blue tent—at that moment shading his wife, their toddler twins and his niece—exceeded the 3-foot limit. Mr. Haas took the news well and even laughed about being busted. An assistant principal at a high school, he knows about rule-following.

Moments later, the 25-year-old Mr. Tartal, who is a lifeguard in addition to Capt. Buckson’s beach patrol deputy, told Marjorie Danko, a receptionist from Hershey, Pa., that the $40 three-sided tent she bought for her grandchildren didn’t pass muster, either.

“I don’t understand this,” she said. “I think umbrellas are much more dangerous. What kind of ordinance is that? I mean, really dumb.”